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Here, we present a protocol for active site validation of metal-organic framework catalysts by comparing stoichiometric and catalytic carbonyl-ene reactions to find out whether a reaction takes place on the inner or outer surface of metal-organic frameworks.
Substrate size discrimination by the pore size and homogeneity of the chiral environment at the reaction sites are important issues in the validation of the reaction site in metal-organic framework (MOF)–based catalysts in an enantioselective catalytic reaction system. Therefore, a method of validating the reaction site of MOF-based catalysts is necessary to investigate this issue. Substrate size discrimination by pore size was accomplished by comparing the substrate size versus the reaction rate in two different types of carbonyl-ene reactions with two kinds of MOFs. The MOF catalysts were used to compare the performance of the two reaction types (Zn-mediated stoichiometric and Ti-catalyzed carbonyl-ene reactions) in two different media. Using the proposed method, it was observed that the entire MOF crystal participated in the reaction, and the interior of the crystal pore played an important role in exerting chiral control when the reaction was stoichiometric. Homogeneity of the chiral environment of MOF catalysts was established by the size control method for a particle used in the Zn-mediated stoichiometric reaction system. The protocol proposed for the catalytic reaction revealed that the reaction mainly occurred on the catalyst surface regardless of the substrate size, which reveals the actual reaction sites in MOF-based heterogeneous catalysts. This method for reaction site validation of MOF catalysts suggests various considerations for developing heterogeneous enantioselective MOF catalysts.
MOFs are considered a useful heterogeneous catalyst for chemical reactions. There are many different reported uses of MOFs for enantioselective catalysis1,2,3,4,5,6,7,8,9,10,11,12,13,14,....
1. Preparation of (S)-KUMOF-1 crystals in three sizes
NOTE: Each step follows the experimental section and supplementary information of previous reports2,24,27. Three different sizes of (S)-KUMOF-1 were prepared: large (S)-KUMOF-1-(L), medium (S)-KUMOF-1-(M), and small (S)-KUMOF-1-(S) with pa.......
The enantioselective carbonyl-ene reaction using the Zn reagent is stoichiometric because of the difference in the binding affinities of the alkoxy and carbonyl groups to the metal (Figure 2). For this reason, the substrates were converted into the products at the reaction site and remained there. The desired products were obtained by dismantling the crystals, as detailed in section 4 of the protocol. The results of the heterogeneous enantioselective carbonyl-ene reaction of substrates by Zn.......
After the synthesis of (S)-KUMOF-1, crystals in some vials seem to be powdery and are not appropriate for use in catalysis. Therefore, proper crystals of (S)-KUMOF-1 need to be selected. The yield of (S)-KUMOF-1 is calculated using only those vials in which it was successfully synthesized. When withdrawn from the solvent, (S)-KUMOF-1 dismantles. Therefore, the crystals should always be kept wet. For this reason, weighi.......
This work was supported by a National Research Foundation of Korea (NRF) Basic Science Research Program NRF-2019R1A2C4070584 and the Science Research Center NRF-2016R1A5A1009405 funded by the Korea government (MSIP). S. Kim was supported by NRF Global Ph.D. Fellowship (NRF-2018H1A2A1062013).
....Name | Company | Catalog Number | Comments |
Acetone | Daejung | 1009-4110 | |
Analytical Balance | Sartorius | CP224S | |
Copper(II) nitrate trihydrate | Sigma Aldrich | 61194 | |
Dichloromethane | Daejung | 3030-4465 | |
Dimethyl zinc | Acros | 377241000 | |
Ethyl acetate | Daejung | 4016-4410 | |
Filter paper | Whatman | WF1-0900 | |
Methanol | Daejung | 5558-4410 | |
Microwave synthesizer | CEM | Discover SP | |
Microwave synthesizer 10 mL Vessel Accessory Kit | CEM | 909050 | |
N,N-Diethylformamide | TCI | D0506 | |
N,N-Dimethylaniline | TCI | D0665 | |
n-Hexane | Daejung | 4081-4410 | |
Normject All plastic syringe 5 mL luer tip 100/pk | Normject | A5 | |
Pasteur Pipette 150 mm | Hilgenberg | HG.3150101 | |
PTFE tape | KDY | TP-75 | |
Rotary Evaporator | Eyela | 243239 | |
Shaker | DAIHAN Scientific | DH.WSO04010 | |
Silica gel 60 (230-400 mesh) | Merck | 109385 | |
Synthetic Oven | Eyela | NDO-600ND | |
Titanium isopropoxide | Sigma Aldrich | 87560 | |
Vial (20 mL) | SamooKurex | SCV2660 | |
Vial (5 mL) | SamooKurex | SCV1545 |
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